As noted in §6, the epiphenomenalist worry arises from
two points that are absolutely basic to Anomalous Monism—first,
that mental events are at the same time physical events, and, second,
that while mental predicates cannot figure into strict causal laws,
physical predicates must. Early criticisms moved very quickly
from these points to the claim that mental properties were causally
irrelevant relative to physical properties. Though it eventually
became clear that this particular concern can get no traction within
Davidson's framework, it is instructive to follow out the line of
argument. An early critic of Anomalous Monism, Ted Honderich (Honderich
1982—for related literature, see Campbell 2003), articulates
the worry by arguing, first, that not all properties of an event are
casually relevant to its effect. For instance, the color of a piece of
fruit has no effect on its measurement—when the fruit is placed
on a scale, the subsequent movement of the weight indicator is not
influenced by the fruit's color. According to Honderich, the color is
therefore a causally irrelevant property of the event (of placing the
green fruit on the scale), while the weight of the fruit is a causally
relevant property. Honderich then asks: what accounts for this
distinction between causally relevant and irrelevant properties? And he
claims that only properties that figure in strict laws—physical
properties—are candidates for casual relevance. There is no
strict lawlike relation between being green and the resulting
measurement, while, according to Honderich, there is such a relation
between the weight of the fruit and that measurement.

Honderich thinks that this simple point generalizes and shows that,
within the framework of Anomalous Monism, mental properties are not
causally relevant because they are not lawlike. His argument can be
understood as follows: since Anomalous Monism insists that mental
events have physical properties that can be related, by strict law, to
the effects of those events, and also insists that such events' mental
properties cannot be so related, it is only ‘by virtue’ of
its physical (i.e., strict lawlike) properties that a mental event
causes what it does. Its mental properties, and thus its being the
particular kind of mental event that it is, play no role in its causal
powers. Thus, Honderich suggests that the cause-law principle must be
articulated slightly differently—as the Principle of the
Nomological Character of Causally Relevant Properties. This
nomological property principle rules out the causal relevance of anomic
mental properties.

Honderich's argument is instructive for a more general consideration
of the wave of epiphenomenalist criticisms lobbed at Anomalous Monism.
First, Honderich's distinction between causally relevant and irrelevant
properties is completely insensitive to the question of what is being
explained or caused, which effect is under consideration (Macdonalds
1995 and Gibbons 2006 usefully discuss the importance of typing effects
in addressing the epiphenomenalist objections). Consider the fruit
example. While the color of the fruit has no causal relevance to its
measurement, that is not the only effect of the event of putting the
fruit on the scale. The color catches the eye of a customer, bleeds
onto the scale and changes its color, and causes a host of other
effects that are not salient when considering only the effect of the
measurement. Salience is dependent on explanatory interests, and if we
shift those interests, what was an irrelevant property with respect to
one effect may be a relevant property with respect to another (see
§6.2).

Second, Honderich arrives at the view that an event's physical
properties are the only causally relevant ones through reflecting on
Anomalous Monism's insistence on the cause-law principle in light of
the anomalism principle. If mental events must instantiate physical
properties—strict-law properties—and all causal
relations must be covered by strict causal laws, then an event's having
such properties is a necessary condition for standing in causal
relations. Davidson can agree with all of this. However, Honderich
concludes from this that it is only ‘by virtue’ of its
physical properties that an event stands in causal relations. This
‘by virtue’ claim then allows Honderich to move directly to
the conclusion that only physical properties are casually relevant.
What enables (i.e., is necessary for) causation is thus held to
be responsible for causation (for a similar argument, see Kim
1993a, 22). But this is disputable. Not all necessary conditions of some
phenomenon are explanatory conditions—conditions
‘responsible for’ that phenomenon. For example, a person
can talk only if she was born—having been born is thus a
necessary condition of her talking. However, her ability to talk is not
explained by her having been born. It is not ‘by virtue’ of
being born that she can talk, though the former is a necessary
condition of the latter. Davidson himself expresses skepticism about
the intelligibility of his critics' use of the ‘by virtue’
locution in discussing Anomalous Monism (Davidson 1993, 6, 13) (see
further §6.1).

The point that causal explanation is interest-relative, and must be
sensitive to what one wishes to explain, is not novel. But it is a
point that often gets lost in epiphenomenalist criticisms of Anomalous
Monism. However, it is also a point that invites important
questions about the relations and differences between causation and
explanation. As we have seen, Davidson insists on a firm
distinction between causation, which is a metaphysical relation between
particular events independently of how they are described, and
explanation, which concerns events only as they are described in
particular ways. Thus, he is inclined to dismiss the epiphenomenalist
concerns about Anomalous Monism, and the locution of ‘causally
relevant and irrelevant properties’ as based upon a confusion and
certainly a different metaphysical framework than that assumed by
Anomalous Monism. Events themselves—rather than any particular
aspect or property of them—cause other events. Our descriptions
of these events (what we speak of as their aspects or properties)
explain why effects described in certain ways occur. Mental
descriptions explain actions by rationalizing them—making them
intelligible in light of the agent's beliefs and purposes. The mental
event that explains an action by rationalizing it is a cause of that
action—otherwise, as discussed above
(§2.2), there would be no
way of answering the question concerning which of the many mental
events that rationalize some action are the ones that actually
explain its occurrence (see further the supplement on
Explanatory Epiphenomenalism). That mental event is also a
physical event (as is the action it explains), according to Anomalous
Monism, because it stands in causal relations (the interaction
principle), and thus (given the cause-law and anomalism principles)
must instantiate physical (strict-law) properties. But properties
themselves don't cause anything, only instances of properties—and these are the events that bear or instantiate them.

Is this point really responsive to Honderich's concern? It is
instructive to observe how some proponents of Anomalous Monism
(Macdonalds1986) have attempted to defend Davidson from
epiphenomenalist concerns by exploiting the point in the following way.
Honderich has insisted that the only causally relevant properties of
events are strict-law properties. But properties don't cause anything;
only their instances do. And particular, causally interacting mental
events are instances of strict-law properties, according to
the monistic component of Anomalous Monism. (Recalling the discussion
of the ‘because’ argument in
§2.2, since reasons causally
explain actions, and due to mental anomalism, actions must be physical,
the claim that mental events cause physical events is justified.) So
Honderich's nomological property principle must itself be amended to
the Principle of the Nomological Character of Causally Relevant
Instances of Properties. Mental properties are causally
relevant, according to this principle, because their instantiations are
also instances of nomic properties, and nomic properties are paradigm
examples of causally relevant properties.

However, it can reasonably be wondered how this line of thinking is
responsive to the point that appears to be underlying Honderich's
nomological property principle. After all, the issue under
consideration has been whether mental properties are relevant to
explanation (recall the discussion of the color of the fruit). The
Macdonalds' insistence that they are turns on the point that only
instances of properties cause anything. But instances are neither
relevant nor irrelevant. At best, they either have or lack causal
efficacy– they are or are not responsible for bringing about some
effect or other. The Macdonalds have perhaps established that because
physical events are paradigm examples of causally efficacious events,
then since, according the Anomalous Monism, mental events are physical
events, mental events inherit any causal efficacy had by physical
events. But that is quite different than establishing that mental
properties are explanatorily relevant—that an event's being a
mental kind of event matters to the occurrence of any effects
in the world. (The Macdonalds (1995) later acknowledge this and develop
an account of explanatory relevance; for discussion, see the supplement on
Explanatory Epiphenomenalism.)